The invention relates to a honing machine for honing rotationally symmetrical bore holes in workpieces according to the preamble of claim 1.
Honing is a method of cutting by means of geometrically undefined cutters, in which a honing tool performs a cutting movement consisting of two components and there is constant surface contact between one or more cutting material bodies of the honing tool and the inner surface of the bore hole to be machined. The kinematics of an expandable honing tool are characterized by simultaneous execution of a rotational movement, an oscillating lifting movement, proceeding in the axial direction of the bore hole, and an expanding movement, which leads to changing of the effective diameter of the honing tool. A surface structure with crossing machining traces is obtained on the inner surface of the bore hole. Surfaces finished by honing can meet extremely high requirements with respect to dimensional and geometrical tolerances, so that many sliding surfaces that are subjected to great loading in engines or engine components, for example cylinder liners in engine blocks, or inner surfaces of bore holes in housings of injection pumps, are machined by honing.
During honing, the abrasive cutting material bodies are pressed against the inner surface of the bore hole by a pressing force. Along with the effective cutting speed and the type of cutting material bodies, the pressing force is an important machining parameter for influencing the machining result from the machine side. The pressing force can be controlled by the expansion of the honing tool.
In the case of some honing methods there is the desire to be able to set the pressing force as accurately as possible, in order that the honing machining can be controlled while taking the pressing force into account. There are already various proposals for generating a sensor signal proportional to the pressing force with the aid of a force sensor provided at a suitable location and using the signal for controlling the honing process.
DE 35 37 172 C2 discloses a honing machine with a device for controlling the operating pressure of a hydraulically acted-upon actuating part of a honing tool. The hydraulically operated actuating part acts in this case on an expanding cone that is provided inside the honing tool and infeeds the honing sticks in the radial direction against the workpiece to be machined. The force exerted on the expanding cone is measured by means of a force sensor. The operating pressure of the hydraulic device is controlled on the basis of a predetermined force profile. The force sensor is arranged between the hydraulically adjustable actuating part and the expanding cone, a spring also being interposed between the force sensor and the hydraulic actuating part. The force measurement is intended thereby to allow the setting of a defined force profile independently of internal losses in the hydraulic system. Details of the transmission of the signals of the force sensor to the control are not disclosed.
EP 0 575 657 A1 describes honing methods in which it is envisaged inter alia to continuously measure the infeeding force acting on expandable honing sticks during the honing process and feed it as a signal to a control. In a honing machine that is only schematically represented, an infeeding device is provided, connected to the control of the honing machine and connected to a honing tool by way of a load cell. The infeeding device has a threaded spindle, which is movable by motor in the axial direction and is transmitted by way of the load cell directly to an infeed rod, which engages in the honing tool. The measured values of the load cell are fed as a signal to the numerical control of the honing machine by way of a line. Details of the transmission of the signals to the control are not disclosed.
DE 196 06 145 A1 describes a device for expanding a honing tool with at least one infeedable honing face, which has an expanding mechanism for infeeding the tool and a force measuring unit for measuring an infeeding force of the expanding mechanism. The force measuring unit is arranged on a portion of the expanding mechanism that is rotationally at rest. This makes it possible to dispense with a complex transmission of the signals of the force measuring unit between a rotating component and a portion that is rotationally at rest. Furthermore, disadvantages with respect to the stiffness of the expanding linkage can be avoided.
EP 2 000 258 A2 describes a honing method in which the reaction forces that occur when the honing stones are pressed against the inner surface of a bore hole to be machined are measured. The corresponding honing machine has sensors integrated in the honing tool for recording this reaction force. In the case of an exemplary embodiment, sensors for measuring the reaction force are arranged between the honing sticks and the honing stick carriers carrying the honing sticks. Details of the transmission of the sensor signals to the control are not disclosed.